1. Field of the Invention
The present invention relates to a hemming working method of coupling a plurality of panels laminated together and a panel assembly manufacturing method using the hemming working method.
2. Background Art
There is a panel member (for example, door panel) used in a vehicle which is constituted by combining two sheets of panels referred to as an inner panel and an outer panel. It is well known to use hemming working in combining the inner panel and the outer panel. In order to couple the inner panel and the outer panel by using hemming working, a flange portion formed at the outer panel is bent relative to the inner panel and the inner panel is pinched by the flange portion and other portion.
In hemming working, as a method of bending the flange portion of the outer panel, there are known roller hemming working for bringing the flange portion into close contact with the inner panel (Patent Reference 1), and press hemming working for bringing the flange portion of the outer panel into close contact with the inner panel by using press forming (Patent Reference 2).
Further, in the hemming working, in order to promote a strength of bonding the inner panel and the outer panel, it is known to carry out projection welding at a portion to be bonded (Patent Reference 3). Projection welding is a kind of spot welding providing a plurality of projected portions at the inner panel, and a current is made to flow concentratedly to a position of the projected portion to thereby heat and press to bond.
In hemming working carried out prior to projection welding, it is necessary to prevent the projected portion from being crushed. That is, when a roller is rolled in roller hemming working, it is necessary to reduce a press force at a position of the projected portion or reduce the press force to the projected portion by moving the roller in a direction of being separated from the inner panel. Further, in press hemming working, it is necessary to reduce or nullify the press force to the projected portion by forming a recessed portion at a position of the flange portion in correspondence with the projected portion.    [Patent Reference 1] JP-A-2007-030041    [Patent Reference 2] JP-A-2006-061931    [Patent Reference 3] JP-A-08-252674
However, when a measure for preventing the projected portion from being crushed as described above is carried out, there is a case in which a sufficient bonding strength by projection welding is not achieved. That is, at a position of the projected portion, the flange portion cannot strongly be pressed to the inner panel, and therefore, the flange portion is brought into a state of being floated up from the projected portion. Further, when the position of the projected portion is pressed by a welding electrode under the state, a region of bringing the projected portion and the flange portion into contact with each other is narrowed, and therefore, a welding range is reduced, and a sufficient bonding strength cannot be achieved (refer to columns of the related art of FIG. 9 and FIG. 10). Further, the contact region is narrowed as described above, and therefore, sputtering is easy to be brought about in projection welding. Further, in roller hemming working, the roller is rolled by reducing a force of pressing the projected portion, and therefore, there is a case in which an edge of bending the flange portion is considerably bulged at the portion of the projected portion to pose a problem in view of an appearance thereof.